东营凹陷油气成藏期次及其分布规律研究

A study on periods of hydrocarbon accumulation and distribution pattern of oil and gas pools in Dongying depression

东营凹陷发育了咸水湖相沙河街组四段上部烃源岩和半咸水深湖相的沙河街组三段下部烃源岩两套有效烃源岩。根据原油的地球化学特征和储层流体包裹体等资料 ,将油气藏的形成分为两个大的阶段 :第一期为早第三纪东营期末 ,凹陷中心的沙河街组四段上部烃源岩已进入生油门限并开始排烃 ,后由于喜山运动使全区遭受抬升和剥蚀 ,油气生成过程中断 ,原油的生物标志化合物组成表明 ,此阶段的原油成熟度较低 ,油气生成数量有限 ;第二期为晚第三纪至第四纪沉积时期 ,伴随着凹陷的持续全面沉降和深埋 ,沙河街组三段下部和沙河街组四段上部烃源岩进一步成熟 ,生烃作用增强 ,原油的成熟度较高。两次成藏的原油分布具有明显的规律性 :凹陷边缘油藏的原油主要来自沙河街组四段上部烃源岩 ,原油成熟度较低 ,是早期充注成藏的 ;生油凹陷中心油藏的原油主要来自沙河街组三段下部烃源岩 ,原油成熟度较高 ,为第二期充注成藏的 ;而过渡带 (斜坡带 )油藏的油气来源及成藏期比较复杂 ,总体特征是混源聚集。

Two sets of active source rocks, the saline lake facies in the upper part of the 4 th member of Shahejie Formation and the brackish deep lake facies in the lower part of the 3 rd member of Shahejie Formation, have been developed in Dongying depression.Based on analysis of crude geochemical features and reservoir fluid inclusion,hydrocarbon accumulations have been formed in two different periods.In the first period,at the end of Dongying epoch in Paleogene,the source rocks in the upper part of the 4 th member of Shahejie Formation in the depression center entered the oil threshold and began discharging hydrocarbons.Hydrocarbon generation was then disrupted due to the uplifting and erosion caused by Himalayan movement.The biomarker components in the crude indicate that oil maturity was low and the amount of hydrocarbons generated was limited in this period.In the second period,Neogene to Quaternary, along with successive and overall subsidence,the deeply buried source rocks both in the lower part of the 3 rd member and in the upper part of the 4 th member of Shahejie Formation would further be matured with intensifying hydrocarbon generation and relatively high oil maturity.Distribution patterns of crude oil generated in these two periods are obvious different.Oil reservoirs with low maturity on the edge of depression were mainly generated from the upper part of the 4 th member of Shahejie Formation and accumulated in the first period; while that with high maturity in the center of depression were generated from the lower part of the 3 rd member of Shahejie Formation and accumulated in the second period.Hydrocarbons in reservoirs in the transitional zone(slope zone)came from multi sources and accumulated in multi periods.